Materials and devices built with smaller and smaller building blocks exhibit unforeseen properties for optical, thermal, electrical, and medical applications. In a large majority of these applications such as high technology devices and biomedical applications, the enhanced functionality is a result of using ultra-fine (less than 1 μm) and, increasingly, nano-scale (less than 100 nm) powders as starting materials or as the enabling component. In the production of these powders in a gas environment, it is important to collect the particles in an efficient manner. It is also necessary to “classify” or separate the desired particle size from other sizes that may be a byproduct of the process to assure only small variances. This means that strategies are needed for removal of agglomerates, classification, and collection.
Current commercial applications where ultra-fine-particles have a significant impact include pigments, toners, sunscreens, solid lubricants, magnetic recording media, electronics devices, ceramic fabrication, and pharmaceuticals. It is expected that the use of ultra-fine powders in nano-technology will substantially grow in the near future.
The technology of “impact type gas particle separators” provides robust performance for collection of powders in the 10 μm diameter range. Impact separators incorporate arrays of aerodynamic surfaces, which intercept the particle-laden gas flow. These surfaces alter the direction of the gas flow with such high acceleration that the particle inertia prevents it from following the gas. Thus the particle pathways and the gas streamlines diverge and the particles are separated. However, ultra-fine and nano-scale particles have a high ratio of aerodynamic drag to inertia, and do not readily separate from the gas flow. Therefore, powders with diameters less than 1 μm cannot be readily collected or classified with impact separators.